This invention relates to a rotary printing head capable of being mounted on a portable labeling machine, a desk-type label printing machine, or the like.
In conventional rotary printing heads, rotation wheels directly or indirectly engage respective printing type support rings. Rotation of the rotation wheels selects and positions for printing particular ones of types that are formed on the outer surfaces of the type rings.
In prior art type positioning mechanisms, the abovementioned type support rings are rotatably carried by a supporting shaft. A plurality of small blind holes are formed in the outer surface of the supporting shaft. Minute coil springs, with steel balls atop them, are fitted into the blind holes. Correspondingly positioned recesses are formed in the inside surfaces of the type rings. These are engaged by the spring-actuated steel balls on the supporting shaft.
However, the assembly of the above described mechanisms is difficult because many minute parts must be handled. The production cost is thus high. In addition, the coil springs and steel balls are liable to be lost during the assembly or later disassembly. Further owing to its structure, it is difficult to form a plurality of the above described ring and shaft engagement arrangements in every type ring. Usually, therefore, only one engaging portion is formed in each type ring. This unfortunately causes the engagement between the above-mentioned recesses and steel balls to be comparatively unstable. Accurate positioning of the type rings is not obtained.
In addition, when an excessive quantity of ink is supplied to the type faces, it interferes with the rotation of the type rings. A plurality of the type rings are held on their supporting shaft in side-by-side relation. The excess ink enters into the gaps between adjacent type rings and into the above described recesses inside the type rings. The ink erodes the above-mentioned coil springs and steel balls that are secured between the type rings and the supporting shaft.